This invention pertains to the art of electric lamps, and more particularly to incandescent lamps. The invention is applicable to three-way incandescent lamps and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications in other lamp environments and applications.
Three-way lamps are well known in the industry, the general characteristics of which are described in detail in commonly assigned U.S. Pat. Nos. 3,131,986; 4,556,822; and, 4,605,877. Three-way lamps have a first or minor filament and a second or major filament so that three distinct light levels can be obtained by selectively providing current to the filaments individually or conjunctively.
FIGS. 1-4 of the attached drawings illustrate a prior art three-way lamp and associated lamp socket. These FIGURES are generally intended to illustrate some of the problems associated with known three-way lamp arrangements. Briefly, and with reference to FIGS. 1-4, a conventional three-way lamp A has an envelope or bulb B formed of a light transmissive material such as glass. Enclosed within the envelope are a first or minor filament C and a second or major filament D. Although the filaments are shown in generally parallel relation to one another, and generally parallel to a longitudinal axis E of the lamp, it will be recognized that other orientations of the filaments can be used with equal success. For example, one filament may be disposed in a horizontal direction and the other filament in a vertical direction.
The filaments are connected to a power source (not shown) by first, second, and third lead wires 10, 12, 14, respectively. Of course it will be recognized that the use of four lead wires as represented in phantom by a fourth lead wire 10' can be used as an alternative to the three lead wire arrangement shown in solid lines. The first lead wire is common to both filaments and extends through a glass stem 16 for connection with a generally cylindrical, electrically conductive metal shell or base 20. Usually the connection of the first lead wire to the shell is provided at a fuse area 22 adjacent the envelope and located at a first end of the shell so that the connection will not interfere with an externally threaded portion 24 of the shell. If a four lead wire configuration is used, the first lead wire 10 is only connected to the first filament C and the fourth lead wire 10' is connected to the second filament D. Both the first and fourth lead wires are then secured to the shell as described above.
As is known, the threaded portion of the shell permits the lamp to be screwed into an associated socket 26 (FIG. 3). The socket includes an internally threaded portion 28 that matingly receives the threaded shell therein. Additionally, the socket has a center contact or eyelet contact 30 and an intermediate contact or tang 32. The center contact 30 is spring loaded in the socket and centrally aligned along a longitudinal axis F that coincides with the longitudinal axis of the lamp when received in the socket. The tang 32 is offset or radially spaced from the axis F as is represented by numeral 34. The tang is also offset in an axial direction as represented by numeral 36 for reasons which will be described in greater detail below.
The second lead wire 12 is connected at one end to the minor filament C. It extends through the glass stem and is connected at its other end to a generally annular or ring-shaped contact member 40 (FIGS. 2 AND 4). The contact member 40 is axially spaced and electrically insulated from the shell 20 by an insulating material 42. An opening (not shown) is provided through the insulating material 42 to allow the second lead wire to extend therethrough for connection with the contact member 40. A dome-like or angled surface 44 extends radially inward from a peripheral rim 46 of the contact member. According to the prior arrangement, the angled surface 44 is pierced to form an opening that receives the second lead wire. Solder 48 is then placed over the end of the lead wire to electrically and mechanically connect the second lead wire to the contact member 40.
Further, the third lead wire 14 extends from a second end of the major filament D, through the glass stem 16 for connection with an eyelet 52 (FIG. 2). The eyelet is axially spaced from the contact member 40 by an insulating material 54. A central opening in the eyelet receives the third lead wire therethrough and the terminal end of the lead wire is then mechanically and electrically connected to the eyelet by solder 56.
Although commercially successful, problems have been experienced with this prior art arrangement. For example, as the lamp is threaded into the associated socket 26, the fixed tang 32 can plow into the solder 48 if an excess amount of solder remains on the angled surface 44 as represented in FIG. 4. As the tang plows into the solder, it inhibits proper and full threading of the lamp into the associated socket. Because of the resistance developed from this plowing action, a consumer believes that full threaded advancement of the lamp into the associated socket has occurred. On the contrary, the desired force of contact between the tang 32 and the contact member 40, as well as between the center contact 30 and the eyelet 54, is not achieved.
Moreover, since the desired electrical contact between the tang and the contact member is not achieved, an arc can develop between the tang and the solder. Since lead solder easily oxidizes, an oxidation layer is formed from the heat due to the undesirable arcing. The oxidation layer limits and inhibits electrical flow or contact. This arrangement is unacceptable for the high in-rush current required by the incandescent lamp. Therefore, electrical connection between the contact member 40 and the tang 32 is desired, instead of establishing electrical contact between the tang and the solder.
Thus, it has been desirable to provide a contact member that provides for consistent metal-to-metal contact between the tang and the contact member, avoids the plowing problem associated with excess solder in the prior lead wire connection arrangement, and addresses still other concerns. For example, the lead wire opening in the prior art arrangement is formed during assembly of the lamp base. That is, the contact member is pierced along the angled surface through use of a tapered pin (not shown). Occasionally this piercing operation develops a rough edge that (i) may not be sufficiently bent back away from the opening, (ii) may be misshapen and compressed back through the opening, or (iii) the portion of the insulating glass that usually covers the pierced edge has been removed. Any one of these problems could potentially hinder proper threading of the second lead wire through its formed opening.
One proposed solution to selected ones of the problems identified above has been suggested by U.S. Pat. No. 2,999,220. That patent discloses a three-way lamp base in which the annular contact member provides a series of outwardly projecting bosses. A lead wire aperture is surrounded by an inward, dome-shaped recess. In an alternate embodiment, a C-shaped embossment is provided on the contact member. According to the arrangements disclosed in the '220 patent, the contact member configuration is intended to reduce the exposed height of the lead wire connection in an effort to establish electrical contact with the intermediate tang.
Therefore, while in some respects the '220 patent would appear to suggest a solution to some of the problems discussed above, it is still deemed deficient in many respects. For example, it does not completely address the desired electrical connection between the contact member and the intermediate tang of the associated socket. That is, radial location of the tang has been known to vary, and in fact is recognized under American National Standards Institute (ANSI) as having variable locations. Accepted variation in dimension 34 of the tang can range from 0.205 to 0.260 inches. The narrow C-shaped embossment or one or more projecting bosses as disclosed in the '220 patent would not assure contact between the tang and the contact member when faced with varied location of the tang.
Moreover, the '220 patent does not assure that the tang electrically contacts the contact member. That is, the electrical connection may be established between the solder associated with the lead wire connection and the tang if the final location of the lamp positions the tang over the lead wire recess in the contact member.
These and other desirable features are not adequately addressed by the prior art.